UNIVERSITY    OF    CALIFORNIA  Agricultural  Experiment  Station 

BENJ.    IDE    WHEELER,    President 

COLLEGE   OF  AGRICULTURE  THomas  forsyth   hunt,  dean  and  doctor 

___!-_.    _v  H      E.    VAN     NORMAN,    Vie  E-  Dl  R  ECTOR 

DbnfXLLbT  and  Dean    University    Farm    School 

CIRCULAR  No.  131 

(June,  1915) 

SPRAYING  FOR  THE  CONTROL  OF  THE 
WALNUT  APHIS* 

By  A.  E.  TYLOR 


DISTRIBUTION 

The  European  walnut  aphis  (Chromaphis  juglandicola)  is  said  to 
occur  in  all  parts  of  the  world  where  the  English  or  Persian  walnut 
tree  is  grown.  In  California  it  has  been  found  in  all  the  walnut 
sections  and  even  on  a  few  isolated  trees  in  the  Sierra  Madre  Moun- 
tains, many  miles  from  any  commercial  orchards. 

INJURY 

During  certain  years,  such  as  the  season  of  1914,  the  walnut  trees 
may  develop  and  mature  their  crop  of  good  sized,  clean  nuts  with  no 
apparent  injury  resulting  from  the  walnut  aphis.  Due  to  their  rela- 
tively small  number  and  their  habit  of  feeding  only  on  the  under 
side  of  the  foliage,  the  aphides  are  not  observed  in  some  seasons 
by  many  of  the  walnut  growers.  In  other  years,  however,  such  as  the 
season  of  1913  and  the  two  preceding  seasons,  when  climatic  conditions 
are  especially  favorable  for  their  development  the  aphis  may  become 
so  numerous  in  a  comparatively  short  time  as  to  become  an  important 
factor  in  the  quality  of  the  nut  crop  harvested. 

The  honeydew  given  off  by  these  insects  falls  on  to  the  upper 
surfaces  of  fruit  and  foliage  below  and  becomes  a  medium  for  the 
growth  of  the  sooty  mold  fungus,  so  that  in  years  of  severe  infestation 
both  nuts  and  leaves  become  coated  with  a  black,  sticky  material.  The 
size  of  the  nuts  may  be  considerably  reduced  and  a  large  percentage 
of  the  crop  consists  of  small-sized,  low-priced  nuts.  The  fact  that 
' '  perforations, ' '  a  term  applied  to  nuts  with  a  defectively  formed  shell, 
are  also  numerous  during  the  years  when  the  aphis  infestation  is  severe 
has  also  been  noticed  by  many  growers.  Whether  or  not  the  loss  of 
plant  juices  and  consequent  drain  upon  the  tree  by  the  aphis  is  the 
actual  cause  of  "perforation"  has  not,  however,  been  proven. 

*  Paper  No.  4,  Citrus  Experiment  Station,  College  of  Agriculture,  University 
of  California,  Riverside,  California. 


LIFE  HISTORY 

The  following  studies  were  carried  on  in  the  Whittier  section  of 
Southern  California:1 

Stem  Mothers. — During  the  spring,  about  the  time  the  walnut  trees 
are  coming  into  leaf,  the  aphis  eggs,  which  were  deposited  on  the  bark 
of  branches  or  twigs  during  the  preceding  fall,  hatch  into  young 
aphides  or  stem  mothers.  In  the  San  Jose  section,  Mr.  Davidson 
reports  finding  these  stem  mothers  emerging  from  the  egg  on  the  early 
varieties  of  walnuts  as  early  as  February  15.  During  the  spring  of 
1914,  the  first  aphides  seen  in  the  Whittier  and  contiguous  sections 
were  found  at  La  Habra  in  the  first  week  of  April,  when  the  early 
varieties  and  seedling  walnut  trees  were  fairly  well  in  leaf. 

The  stem  mothers  produce  viviparously  the  winged  females,  which 
in  turn  produce  living  young.  It  is  this  form  of  the  aphis  which 
increases  in  numbers  during  the  spring,  and,  by  July  or  late  summer, 
may  heavily  infest  the  under  side  of  the  walnut  foliage.  In  one 
severely  infested  orchard  near  the  coast  200  aphides  were  counted  on 
a  single  medium-sized  leaflet  on  July  16,  1914,  a  year  in  which  the 
infestation  did  not  become  severe  except  in  a  few  instances. 

Number  of  Moults. — During  the  process  of  development  the  nymphs 
moult  four  times.  In  July  and  September,  at  least,  the  first  moult 
occurs  usually  in  from  four  to  six  days  after  birth ;  the  second  in  six 
to  eight  days;  the  third  in  eight  to  ten,  or,  in  rare  cases,  in  twelve 
days;  the  fourth  and  last  moult  occurs  in  from  eleven  to  fourteen 
days  from  birth. 

Time  of  Development. — From  the  fourth  or  last  moult  the  nymph 
emerges  as  a  winged  adult  female.  The  number  of  days  passed  from 
birth  to  maturity  during  July,  1914,  in  the  Whittier  section  varied 
from  eleven  to  fourteen  days,  the  greatest  number  of  individuals 
maturing  in  twelve  days. 

The  length  of  time  required  to  reach  maturity  may  vary  in  dif- 
ferent sections,  probably  depending  upon  the  climatic  conditions. 
Davidson  found  during  the  month  of  July,  1911,  at  San  Jose,  that  this 
time  varied  from  fourteen  to  nineteen  days,  the  majority  maturing  in 
sixteen  days. 


i  The  life  history  of  this  and  closely  related  species  of  walnut  aphides  has  been 
studied  in  detail  by  Mr.  W.  M.  Davidson  in  the  San  Jose  section  of  California  and 
published  in  Bulletin  100,  Bur.  Ent.,  U.  S.  D.  A. 


Number  of  Young  Produced. — During  July,  1914,  many  aphides 
were  placed  in  leaf  cages  and  the  number  of  offspring  from  each  adult 
noted.  The  average  number  of  young  produced  per  adult  female  was 
41,  the  largest  number  of  young  produced  by  any  one  adult  being  59. 
During  September  and  October  similar  records  were  obtained  and  at 
this  time  the  average  number  of  offspring  from  one  adult  was  37,  and 
in  one  case  an  adult  produced  46  young.  The  adults  lived  from  thirty 
to  thirty-five  days  and  produced  young  almost  up  to  the  time  of  their 
death. 

The  number  of  generations  per  year  of  the  walnut  aphis  has  not 
been  definitely  determined  for  Southern  California.  In  the  San  Jose 
section  there  are  ten  and  possibly  eleven.  Aphides  may  be  found  on 
the  foliage  until  the  latter  drops  in  the  winter.  The  number  of  pos- 
sible progeny  resulting  from  a  single  stem  mother  during  the  season, 
therefore  (estimating  35  young  per  female  and  ten  generations),  would 
be  about  78,000,000,000,000. 

Oviparous  Form. — During  the  late  summer  and  fall  the  oviparous 
form  or  egg-laying  stage  of  the  walnut  aphis  appears.  The  female 
of  this  form  differs  in  appearance  from  the  winged  viviparous  adults, 
principally  in  being  wingless  and  having  two  lateral  black  bands  on 
the  back.  They  do  not  form  a  distinct  generation,  but  from  July  to 
and  including  the  fall  and  until  the  leaves  drop  in  the  winter  a  portion 
of  the  young  aphides  may  develop  into  the  oviparous  form,  the  wing- 
less female,  and  also  the  winged  male.  This  is  the  egg-laying  stage 
of  the  walnut  aphis,  and  after  fertilization  the  female  goes  to  the 
twigs  or  branches,  where  the  eggs  are  deposited  in  old  leaf  scars,  in 
crotches,  or  on  the  bare  surface  of  the  bark.  In  the  egg  stage  the 
aphis  winters  over  on  the  old  twigs,  branches,  or  trunk,  and  in  the 
spring,  with  the  leafing  out  of  the  trees  the  eggs  hatch,  producing  the 
stem  mothers,  and  the  life  cycle  is  completed. 


WINTER  CONTROL  OF  WALNUT  APHIS 

During  February  and  March  of  1913.  and  again  in  1914,  Professor 
R.  E.  Smith  and  his  associates  carried  on  spraying  experiments  in 
Ventura  and  Santa  Barbara  counties  for  the  control  of  the  walnut 
blight  and  incidentally  for  the  winter  control  of  the  walnut  aphis.2 
Power  outfits  and  the  M.  A.  C.  nozzles  were  used.  By  maintaining 
at  least  200  pounds  pressure  they  were  able  to  spray  thoroughly  the 
highest  trees  from  the  ground  with  these  nozzles. 


2  See  Circular  107,  Univ.  of  Cal.  Agr.  Exp.  Sta. 


The  following  spray  was  found  very '  effective  in  destroying  the 
aphis  eggs  on  trunk,  limb,  and  branch  when  these  were  thoroughly 
covered  with  the  solution: 

Commercial  lime-sulfur  5  gals. 

Quicklime  25  lbs. 

Water  95  gals. 

Twenty-five  gallons  of  spray  were  applied  to  average  sized  trees  ten 
years  of  age.  This  cost  45  cents  per  tree.  For  very  large  trees  40 
gallons  per  tree  were  applied,  costing  72  cents  per  tree.  This  includes 
total  expense  of  materials  and  application. 


RESULTS  OF  WINTER  SPRAYING  IN  19143 

During  the  second  season  of  winter  spraying  with  lime-sulphur  the  work 
which  cost  45  cents  per  tree  in  1913  was  accomplished  for  30  cents  per  tree,  by 
reason  of  greater  efficiency  and  improved  methods.  As  to  the  results  of  the 
work,  it  may  be  said  that  both  in  1913  and  1914  aphides  were  well  controlled  by 
the  winter  spray  and  only  developed  upon  the  sprayed  trees  by  blowing  in  from 
the  outside  later  in  the  season.  The  results  of  aphis  control  were  markedly 
different  upon  trees  which  received  abundant  irrigation  and  those  which  had 
no  irrigation.  Upon  well  irrigated  trees  the  effects  of  the  spraying  were  not 
very  pronounced,  even  when  the  insect  became  abundant  upon  unsprayed  trees 
of  the  same  kind.  Upon  unirrigated  orchards,  however,  and  especially  during 
the  dry  season  of  1913,  very  decided  benefit  could  be  seen  from  the  spraying. 
This  benefit  showed  itself  by  increased  growth  of  the  trees  over  those  unsprayed 
and  holding  of  the  foliage  later  in  the  season.  The  latter  was  especially  marked 
after  the  extremely  hot,  dry  wind  of  September,  1913,  which  almost  defoliated 
the  unsprayed  trees  which  had  been  heavily  attacked  by  aphis,  while  the  sprayed 
trees  still  retained  much  green  foliage. 

In  regard  to  the  crop,  no  decided  effect  in  quantity  was  seen  during  the 
season  of  spraying,  but  the  effect  upon  quality  was  quite  marked,  the  percentage 
of  culls  being  decidedly  less  upon  the  sprayed  trees.  During  the  second  season 
after  spraying  and  aphis  control,  the  crop  of  the  sprayed  trees  increased  decid- 
edly in  quantity,  the  gain  being  due  apparently  to  increased  growth  during  the 
year  of  the  spraying. 

The  following  table  gives  three  years'  records  of  this  orchard: 

Crop  Record,  Robert  Main  Ranch,  Goleta,  1912 


Plot 

1 

No.  trees 
258 

Good 
nuts,  lbs. 

3690 

Good 
nuts  per 
tree,  lbs. 

14.3 

Culls, 
lbs. 

767 

Per  cent 
culls 

17 

Spray 
None 

2 

227 

3381 

15.0 

535 

13y2 

None 

3 

165 

1509 

9.15 

203 

12 

None 

3  This  discussion  on  the  results  of  winter  spraying  in  1914  has  been  prepared 
by  Professor  R.  E.  Smith  of  the  Division  of  Plant  Pathology  and  has  been  intro- 
duced here  to  supplement  data  published  in  Circular  107  of  this  Station. 


Fig.  1. — Spraying  walnut  trees  for  the  control  of  the  walnut  aphis. 
M.  A.  C.  nozzle  adjusted  for  spraying  the  lower  half  of  the  tree. 


Crop  Record,  Robert  Main  Ranch,  Goleta,  1913 


'lot 

1 

No.  trees 
258 

Good 

nuts,  lbs. 

7250 

Good 
nuts  per 
tree,  lbs. 

28.0 

Culls, 
lbs. 

1739 

Per  cent 
culls 

19 

Spray 
None 

2 

227 

6773 

30.0 

1179 

15 

None 

3 

165 

2516 

15.25 

268 

9% 

Lime-sulphur 

Crop  Record,  Robert  Main  Ranch,  Goleta,  1914 


Plot 

1 

No.  trees 
258 

Good 

nuts,  lbs. 

6835 

Good 
nuts  per 
tree,  lbs. 

26.5     -I 

Culls,            Per  cent 
lbs.                 culls 

Very  few  culls  this 

Spray 
r      Lime-sulphur 

2 

227 

7005 

30.0 

year 
Crop  ran: 

18.7%  Jumbo       «- 
77.05  No.  1 
4.25  No.  2 

Lime-sulphur 

3 

165 

5190 

31.5    , 

Lime-sulphur 

This  twenty-acre  orchard  was  divided  into  three  plots  and  the  crop  record 
of  1912,  the  year  before  spraying  commenced,  was  obtained  in  order  to  get  an 
idea  of  the  average  run  of  the  orchard.  The  crop  of  that  year,  however,  was 
only  about  half  of  the  average  in  quantity.  The  trees  in  the  plot  chosen  for 
spraying,  No.  3,  were  below  the  others  in  size,  the  poorest  part  of  the  orchard 
being  purposely  taken.  In  March,  1913,  Plot  3  was  sprayed  with  lime-sulphur; 
the  other  two  plots  remained  unsprayed.  The  new  growth  was  coming  out 
somewhat  when  Plot  3  was  sprayed  and  received  some  injury  from  the  appli- 
cation. This  possibly  accounts  for  the  fact  that  the  increase  in  crop  over  1912, 
as  shown  in  the  column  headed  ' '  Good  nuts  per  tree, ' '  was  somewhat  less  in 
this  plot  than  in  numbers  1  and  2,  the  increase  of  the  latter  being  about  100 
per  cent,  while  in  Plot  3  it  is  about  70  per  cent.  In  the  column  entitled 
"Percentage  of  culls"  the  effect  of  the  spraying  on  the  quality  of  the  crop  will 
be  seen,  this  percentage  in  the  unsprayed  plots  1  and  2  increasing  somewhat  over 
1912  on  account  of  the  hot  wind  in  September,  while  in  Plot  3  the  percentage 
of  culls  was  materially  decreased  in  spite  of  the  wind.  In  March,  1914,  the 
whole  orchard  was  sprayed  with  lime-sulphur,  but  again  it  will  be  seen  by 
comparing  the  crops  of  plots  1  and  2  in  that  year  with  those  of  the  previous 
season  that  no  increase  in  the  quantity  of  the  crop  was  obtained  from  the 
spraying  during  the  same  season.  The  1914  crop  of  Plot  3  shows  plainly,  how- 
ever, the  effect  of  the  spraying  in  1913.  These  trees  originally  averaged  little 
more  than  half  the  crop  of  those  in  plots  1  and  2,  but  they  have  now  increased 
to  an  extent  which  gives  them  the  heaviest  production  of  the  whole  orchard. 
It  appears  from  the  figures  that  the  crop  of  this  plot  has  been  about  doubled 
as  a  result  of  the  spraying.  This  we  attribute  to  the  increased  growth  of  the 
trees  resultant  upon  the  control  of  aphis  in  this  unirrigated  orchard  during  the 
dry  season  of  1913. 


,  I 


Fig.  2. — Spraying  walnut  trees  for  the  control  of  the  walnut  aphis. 
M.  A.  C.  nozzles  adjusted  for  spraying  the  upper  part  of  the  tree. 


SUMMER  SPRAYING  FOR  THE  WALNUT  APHIS 

There  are  two  chief  objections  to  winter  spraying  for  the  control 
of  walnut  aphis. 

(1)  During  many  seasons  the  aphis  does  not  become  so  numerous 
as  to  cause  any  economic  or  appreciable  injury  to  fruit  or  trees.  It 
is  only  in  certain  years  that  this  insect  becomes  so  serious  a  pest  as 
to  require  control  measures.  In  order  to  check  the  injury  from  the 
aphis  during  these  epidemic  years  with  the  winter  spraying,  however, 
it  is  necessary  to  spray  every  year,  since  the  seasons  of  severe  infes- 
tation cannot  be  forecasted. 

(2)  The  walnut  aphis  spreads  rapidly  by  migration,  so  that  for 
best  results  to  continue  throughout  the  season  from  the  winter  spraying 
large  blocks  or  entire  sections  must  be  sprayed  during  the  dormant 
period. 

For  these  reasons  it  was  deemed  advisable  to  determine  the  effect 
of  summer  spraying. 

During  the  season  of  1914  the  aphides  did  not  become  so  numerous 
in  most  sections  of  Southern  California  as  to  cause  any  serious  injury, 
so  that  the  actual  cash  benefit  to  the  grower  resulting  from  such 
spraying  could  not  be  estimated.  It  has  been  possible,  however,  to 
determine  the  practicability  of  such  spraying,  the  comparative  killing 
efficiency,  the  cost  of  the  several  sprays  tried,  and  the  possible  injury 
to  foliage  resulting  from  the  use  of  these  sprays. 

Equipment. — The  machine  used  for  this  work  was  a  gasoline  power 
outfit  containing  a  200-gallon  tank  and  a  pressure  of  200  pounds  was 
maintained.  Two  50-foot  lines  of  half-inch  hose  and  the  M.  A.  C. 
spraying  nozzles  were  used.  The  ordinary  nozzle  of  the  cyclone  type 
was  also  tried,  but  for  this  work  proved  unsatisfactory.  With  the 
M.  A.  C.  nozzles  the  foliage  of  the  largest  trees  may  be  effectively 
covered. 

In  both  the  El  Monte  and  Anaheim  groves,  where  the  experiments 
were  conducted,  the  trees  are  ten  years  old  and  average  25  to  30  feet 
in  height.  In  each  experiment  an  average  of  six  trees  were  thoroughly 
sprayed  with  200  gallons  of  solution,  or  an  average  of  33 y3  gallons 
of  spray  used  per  tree.  When  both  the  M.  A.  C.  nozzles  were  working 
properly  and  a  pressure  of  upwards  of  200  pounds  maintained  the 
200-gallon  tank  was  emptied  in  from  twenty-five  to  thirty  minutes. 
With  the  refilling  hose,  practically  ten  minutes  were  consumed  in 
refilling  the  tank.  The  time  required  to  drive  from  the  source  of 
water  to  the  place  of  work  was  not  considered  and  may  vary  in  every 


grove.  In  the  spraying  of  large  orchards,  a  supply  wagon  and  extra 
man  to  mix  and  haul  the  spray  from  the  source  of  water  to  the  spray 
machine  in  the  field  should  be  part  of  the  equipment. 

Results. — The  following  is  a  summary  account  of  results  obtained 
from  the  several  sprays  tried  in  the  Killian  and  Neff  orchards.  One 
tank  of  200  gallons  of  each  spray  was  used  and  from  five  to  seven  trees 
covered  in  each  experiment.  Two  rows,  one  on  the  east  and  the  other 
on  the  west  side  of  the  sprayed  rows,  were  left  unsprayed  and  used 
as  checks.  There  were  fewer  aphides  on  the  east  than  on  the  west  side. 
The  results  from  each  experiment,  as  well  as  in  the  two  check  rows, 
were  obtained  by  counting  the  number  of  live  aphides  on  thirty  to 
sixty  terminal  leaflets  (five  to  ten  leaflets  per  tree) . 

Table  Summarizing  the  Work  on  J.  E.  Killian 's  Grove,  El  Monte 


Date  of 

spraying  Materials  used  to 

1914  200  gallons  of  water 

7/27       Black  leaf  40,  1  pt. 

Whale  oil  soap,  4  lbs. 
7/24       Black  leaf  40,  1  pt. 

Liquid  soap,  1  gal. 
7/25       Lime-sulfur  (com.),  2  gals. 

Black  leaf  40,  15  fluid  oz. 

7/25       Spraysect,  1  gal. 

Liquid  soap,  1  gal. 
7/27       Milled  sulfur,  6  lbs. 

Black  leaf  40,  15  fluid  oz. 
7/27       Whale  oil  soap,  12  lbs. 
7/28       Distillate,  2  gals. 

Whale  oil  soap,  4  lbs. 
7/28       Kerosene,  8  gals. 

Liquid  soap,  2  gals. 


Cost  of 

materials 

Date  No.  No.  of         for  200 

examined      of  live       leaflets         gals,  of 

1914         aphides    examined        spray 

$1.80 


7/29 
7/29 
7/29 

7/29 

7/29 

7/29 
7/29 

7/29 


0 

14 

1 

77 

0 

78 
106 

23 


30 
50 
35 

35 

25 

35 

30 

35 


2.06 
1.83 

2.00 


.72 
.36 


Remarks 
..o  injury 

No  injury 

Considerable 
burning  of 
leaves 

No  injury 

No  injury 

No  injury 
Slight  spotting 


1.56       No  injury 


Note. — On  35  terminal  leaflets  of  east  check  row,  122  live  aphides;  on  35  terminal  leaflets 
of  west  check  row,  474  live  aphides. 


Table  Summarizing  Summer  Spraying  Experiments  on  J.  B.  Neff's  Grove,  Anaheim 


Cost  of 

materials 

Date  of 

Date 

No. 

No.  of 

for  200 

spraving 

Materials  used  to 

examined 

of  live 

leaflets 

gals,  of 

1914 

200  gallons  cf  water 

1914 

aphides 

examined 

of  spray 

Remarks 

7/31 

Black  leaf  40,  1  pt. 
Liquid  soap,  1  gal. 

8/1 

0 

60 

$2.06 

No  injury 

7/31 

Black  leaf  40,  1  pt. 
Whale  oil  soap,  4  lbs. 

8/1 

2 

60 

1.80 

No  injury 

7/31 

Spraysect,  1  gal. 
Liquid  soap,  1  gal. 

8/1 

349 

60 

2.00 

No  injury 

7/31 

Whale  oil  soap,  12  lbs. 

8/1 

358 

60 

.72 

No  injury 

7/31 

Distillate,  2  gals. 
Whale  oil  soap,  4  lbs. 

8/1 

307 

60 

.36 

Some  spotting 
of  foliage 

7/31 

Kerosene,  8  gals. 
Liquid  soap,  1%  gals. 

8/1 

310 

60 

-1.37 

No  injury 

Note. — Sixty  terminal  leaflets  on 

north  side  contained  1 

739  live  aphides;  60 

terminal  leaf- 

lets    on    south    side    contained    2298    live    aphides. 
F.  O.  B.,  San  Francisco. 


Spraysect    (prepa-red),    $1.50    per    gallon, 


10 

Trees  that  have  been  pruned  and  thinned  out  can  be  more  thor- 
oughly and  effectively  sprayed  than  those  that  have  never  been  pruned. 
In  the  former  case  the  leaflets  are  larger  and  fully  expanded,  while 
the  leaflets  on  unpruned  trees  are  small,  partly  doubled  up  and  very 
crowded. 

In  years  that  promise  to  be  seasons  of  severe  infestation  the  spray- 
ing should  not  be  delayed  until  the  injury  to  fruit  and  foliage  has 
been  done,  but  should  be  done  in  the  early  summer,  so  as  to  prevent 
the  heavy  infestation  and  resultant  injury. 

The  best  results  obtained  from  the  summer  spraying  were  obtained 
from  those  sprays  containing  black  leaf  40,  and  of  those  tried  the  one 
containing  black  leaf  40,  1  pint,  and  4  pounds  of  whale  oil  soap  is  the 
one  advised  for  use. 

SUMMABY 

Injury. — During  certain  years  of  heavy  infestation  the  English 
walnut  aphis  may  reduce  considerably  the  size  of  the  nuts  and  depre- 
ciate the  quality.  "Perforated"  nuts  may  also  be  due  to  aphis  injury. 
The  drain  upon  the  tree  is  heavy.  Aphis  infestation  may  also  increase 
the  dissemination  of  the  walnut  blight. 

Life  History. — At  the  time  of  leafing  out  of  the  walnut  trees  in 
spring  the  walnut  aphis'  eggs  hatch,  producing  the  stem  mothers. 
The  winged  viviparous  stage  may  be  found  on  the  walnut  leaves  during 
late  spring,  summer,  and  until  the  foliage  falls  in  the  winter.  During 
the  summer  in  the  Whittier  sections  each  viviparous  female  produces 
on  an  average  41  nymphs.  One  female  produced  59  nymphs.  The 
nymph,  in  Southern  California,  requires  about  twelve  days  from  birth 
to  maturity  and  there  are  about  ten  generations  a  year. 

The  sexual  or  egg-laying  stage  does  not  form  any  distinct  gener- 
ation, but  may  be  found  more  or  less  numerous  from  July  to  the  time 
the  leaves  fall.  After  fertilization  the  sexual  females  leave  the  foliage 
and  deposit  their  eggs  in  old  leaf  scars,  in  the  crotches,  or  on  the  bark 
of  twig,  branch,  or  trunk. 

Winter  Control. — The  most  effective  spray  for  the  winter  control 
of  the  walnut  aphis  is  that  recommended  in  Circular  107  of  this 
Experiment  Station,  consisting  of  commercial  lime-sulfur,  5  gallons; 
unslaked  lime,  25  pounds;  water,  95  gallons,  which  costs  about  $2.55 
per  200  gallons  of  spray.  Spraying  should  be  done  before  growth 
starts  in  the  spring.  An  average  of  25  gallons  of  spray  is  required 
for  trees  ten  years  old  and  40  gallons  for  larger  trees. 

Average  cost  of  spraying  for  trees  of  10  years  35  cents 

Average  cost  of  spraying  very  large  trees  75  cents 


11 

The  chief  drawbacks  of  winter  spraying  are  (1)  the  necessity  of 
spraying  every  year;  (2)  rapid  migrations  of  aphis  from  surrounding 
unsprayed  trees. 

Summer  Control. — The  most  efficient  spray  found  for  control  of 
walnut  aphis  during  the  summer  contains  black  leaf  40,  1  pint ;  whale 
oil  soap,  4  pounds ;  water,  200  gallons,  and  costs  $1.80  per  200  gallons 
of  spray,  when  the  materials  are  purchased  in  small  amounts.  About 
30  to  35  gallons  of  spray  are  required  to  thoroughly  covt  r  ten-year-old 
walnut  trees.  The  M.  A.  C.  nozzles  are  the  most  suitalle  ones  found 
for  spraying  walnut  trees. 


STATION  PUBLICATIONS  AVAILABLE  FOR  DISTRIBUTION 


REPORTS 

1897.      Resistant  Vines,   their  Selection,   Adaptation,   and  Grafting.      Appendix  to  Viticultural 
Report  for   1896. 

1902.  Report  of  the  Agricultural  Experiment   Station   for   1898-1901. 

1903.  Report  of  the  Agricultural   Experiment    Station   for    1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station   for   1903-04. 

1914.      Report  of  the  College  of  Agriculture   and  the  Agricultural   Experiment   Station,   July, 
1913-June,  1914. 

BULLETINS 


No. 

168.  Observations    on    Some    Vine    Diseases 

in   Sonoma  County. 

169.  Tolerance  of  the  Sugar  Beet  for  Alkali. 


Studies  in  Grasshopper  Control. 

A  New  Wine-Cooling  Machine. 

A    New   Method    of    Making   Dry    Red 

Wine. 
Mosquito   Control. 
Analysis    of    Paris    Green     and    Lead 

Arsenate.    Proposed  Insecticide  Law. 
The  California  Tussock-Moth. 

184.  Report    of    the     Plant     Pathologist     to 

July   1,    1906. 

185.  Report  of  Progress  in   Cereal   Investi- 
gations. 

The  California  Grape  Root-worm. 
Grape  Culture  in  California;  Improved 

Methods      of     Wine-making;      Yeast 

from   California    Grapes. 
The  Grape  Leaf-Hopper. 
Report    of    the    Plant    Pathologist    to 

July  1,    1909. 

207.  The  Control  of  the  Argentine  Ant. 

208.  The  Late  Blight  of  Celerv. 

211.  How  to   Increase  the   Yield   of  Wheat 

in   California. 

212.  California   White   Wheats. 


170. 
174. 

177. 

178. 
182. 

183. 


195. 
197. 


198. 
203. 


213. 
216. 


220. 
225. 
227. 
230. 
234. 
241. 
242. 
243. 

244. 
246. 

248. 

249. 
250. 
251. 


252. 
253. 


254. 
255. 


The   Principles   of  Wine-making. 

A     Progress     Report  .  upon     Soil    and 

Climatic     Factors      Influencing     the 

Composition  of  Wheat. 
Dosage  Tables. 

Tolerance  of  Eucalyptus  for  Alkali. 
Grape  Vinegar. 
Enological    Investigations. 
Red  Spiders  and  Mites  of  Citrus  Trees. 
Vine  Pruning  in  California.     Part  I. 
Humus  in  California  Soils. 
The  Intradermal  Test  for  Tuberculosis 

in  Cattle  and  Hogs. 
Utilization  of  Waste  Oranges. 
Vine  Pruning  in  California.     Part  II. 
The  Economic  Value  of   Pacific  Coast 

Kelps. 
Stock  Poisoning  Plants  of  California. 
The  Loquat. 

Utilization    of    the    Nitrogen    and    Or- 
ganic  Matter   in    Septic    and    Imhoff 

Tank  Sludges. 
Deterioration  of  Lumber. 
Irrigation   and    Soil   Conditions   in  the. 

Sierra  Nevada  Foothills,  California. 
The  Avocado  in  California. 
The  Citricola   Fcale. 


CIRCULARS 

No.  No. 

65.    The   California   Insecticide   Law.  109. 

69.  The    Extermination    of    Morning-Glor  \ 

70.  Observations    on    the    Status    of    Corn 

Growing  in  California.  110. 

76.    Hot  Room  Callusing.  111. 

79.  List  of  Insecticide  Dealers. 

80.  Bovs'  and  Girls'  Clubs.  113. 

82.  The     Common     Ground     Squirrels     of  114. 

California.  115. 

83.  Potato  Growing  Clubs.  117. 

87.  Alfalfa. 

88.  Advantages  to  the   Breeder  in  Testing  118. 

his  Pure-bred  Cows  for  the  Register  119. 

of  Merit.  121. 

91.  Disinfection   on   the   Farm. 

92.  Infectious    Abortion    and    Sterilitv    in  122. 

Cows. 

100.  Pruning  Frosted  Citrus  Trees.  123. 

101.  Codling    Moth    Control    in    the    Pacra- 

mento  Valley.  124. 

106     r;'-^ct'ons  for  using  Anti-Hog-Cholera  125. 

Serum.  126. 

107.  Spraying  Walnut  Trees  for  Blight  and  127. 

Aphis  Control.  128. 

108.  Grape  Juice.  129. 

130. 


Community  or  Local  Extension  Work 
by  the  High  School  Agricultural  De- 
partment. 

Green  Manuring  in  California. 

The  Use  of  Lime  and  Gypsum  on  Cali- 
fornia Soils. 

Correspondence  Courses  in  Agriculture. 

Increasing  the  Dutv  of  Water. 

Grafting  Vinifera  Vineyards. 

The  Selection  and  Cost  of  a  Small 
Pumping   Plant. 

The  Countv  Farm  Bureau 

Winery  Directions. 

Some  Things  the  Prospective  Settler 
Should  Know. 

The  Management  of  Strawberry  Soils 
in  Pajaro  Vallev. 

Fundamental  Principles  of  Co-opera- 
tion  in   Agriculture. 

Alfalfa  Silage  for  Fattening  Steers. 

Aphids  on  Grain  and  Cantaloupes. 

Spraying  for  the  Grape  Leaf  Hopper. 

House  Fumigation. 

Insecticide   Formulas. 

The  Control  of  Citrus  Insects. 

Cabbage  Growing  in  California. 


